This invention relates to the collection of solar energy for conversion to thermal, electrical or chemical energy. In one mode of operation, solar energy directly heats an absorptive liquid for thermal related processes. Since the liquid itself, is exposed to solar radiation, photo chemical, photoelectrical, photoelectrochemical and photobiological processes are also permitted.
At present, the use of solar energy devices for thermal purposes is severely restricted because of (a) their relatively poor thermal efficiency, (b) the relatively high cost of producing them, and (c) the problems encountered by them under no-flow conditions. Most of the solar thermal devices developed over the past century rely on a metal absorber plate which is heated by the sun's radiation. A fluid confined in a metal flow path is circulated past the absorber plate, indirectly heating the fluid and cooling the plate, and the heat acquired by the fluid is then used for energy related purposes. The fluid generally operates at a pressure several times greater than atmospheric, requiring strong, heavy materials for the fluid flow path. Under no-flow conditions the absorber plate can be heated by the sun to temperatures exceeding 500.degree. F., requiring high temperature materials throughout the device. The extreme temperature range the device must accommodate creates problems in thermal expansion, damage and limited service life. Many solar thermal devices suffer from problems relating to boiling or freezing of the working fluid and chemical attack on the fluid path elements by the working fluid. All of these problems demand the use of expensive, high performance materials and designs.
Poor thermal efficiency of most current designs relates to (a) poor heat conductance from the absorber to the working fluid, (b) partial coverage of the absorber plate by the working fluid, (c) high convective and radiative heat losses during operation, and (d) the high heat capacitance of the materials used causes poor thermal response.
Since most current solars thermal devices do not expose the working fluid to the direct radiation of the sun, they do not adapt to photo-effect processes such as photoelectric and photochemical processes.